Cyclone Lusi: What you need to know

WeatherWatch.co.nz's Philip Duncan answers some of your questions about Cyclone Lusi

Cyclone Lusi continues to slowly churn away near Vanuatu - and will likely rapidly intensify over the next three days as it approaches New Zealand from the north.

How strong will the winds be?
Around the centre of the low we expect sustained winds between gale and hurricane force (basically 65km/h to 120km/h). However the local geography here in New Zealand can boost winds - or reduce them. 120km/h winds blowing over the Kaimai Ranges, for example, can then speed up to 150km/h +. Other ranges can block the winds - all comes down to the intensity of the low and wind angle as it moves in on Saturday/Sunday.

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Where will it be windy?
Most of the North Island will have blustery weather at some point this weekend - not all wiill have gales - but some pockets will likely be exposed to damaging gales. North Island regions west of main ranges are most exposed - so too are all northern regions near the centre of the low. At this stage our main concern for gales will be the eastern Waikato/western Kaimai Ranges, Coromandel Peninsula also parts of Central Plateau, Northland and Auckland.

Will the rain end the dry conditions?
Again it depends on where the centre of the low tracks. Plenty of regions will receive rain from this low - and right now we do expect soaking rains in some of our driest regions. But it may not be until later this week that we can lock in with high confidence those exposed to light rain, heavy rain or missing out altogether. Driest regions in the north of the country will be most exposed to the rain from this low - but it may be too much of a good thing for some areas - rain warnings are likely in our view. This will please many farmers - but may be of concern for those in low lying areas vulnerable to flooding.

When will you be able to lock in more details?
We expect to able to on Wednesday PM and Thursday PM. We also expect MetService to issue more information in the coming days which will help people plan accordingly.

Is it possible severe weather will miss NZ?
As with any tropical low there is always an element of surprise - even for the most experienced meteorologists. There is certainly a chance that weakening of the low combined with a slight direction change could see severe weather risks reduced - but for 9 days that has not been what the various computer models have been predicting. Again we will be able to lock in more around Weds PM / Thurs.

Is this storm going to be big?
Every ex-tropical cyclone is different - even if they look the same as they move in. Bola, Fergus, Drena and Wilma have been the four biggest tropical storms to hit New Zealand since 1988. Sometimes you dont know how significant a tropical storm will be until the day before it arrives/as it's moving in. Other storms have 'died' just 100kms north of Northland. This one doesn't look overly large - but the models do pick it being intense and deep this weekend over northern NZ, before it falls apart on Monday/Tuesday.

Will everyone be exposed to severe weather?
No - in fact we expect some regions/centres to miss out on severe wind and rain - but those who are exposed do have fairly high risks for severe weather.
Who is most exposed to this storm?
The entire North Island and the upper South Island. However severe weather will likely be focused on the north at first, then may slide further south towards the lower North Island - depending on if the storm holds its strength.

Is it guaranteed to hit us?
No one can say with 100% certainty but right now we have 80 - 90% confidence of a direct hit this weekend - but the storm could weaken rapidly once it moves in. However latest models don't support that, they show it taking until Monday to fall apart. This is why we are now doing updates two to three times a day now.

Will it still be a tropical cyclone when it reaches NZ?
No, usually cyclones lose their technical "tropical cyclone" title as they transition out of the tropics and over cooler waters near NZ. This transition changes the structure of the cyclone and is why it can be a little tricky tracking them in advance with high precision - especially in a country as narrow as New Zealand . Regardless of the technicality, Lusi's remnants may still pack similar strengh to Category 1 or 2 tropical storm. Bola, Drena, Fergus and Wilma technically lost their cyclone titles - but 25 years on we still refer to them by their names and call them cyclones.

- WeatherWatch.co.nz

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